Coaxial relay



Jan. 21, 1964 GRAY 3,118,989

COAXIAL RELAY Filed Jan. 31, 1962 IN VENTOR Regina/a 1. Gray BY 22 4g ATTORNEYS United States Patent 3,118,989 CQAXIAL RELAY Reginald llvan Gray, 513 fiampsen Road, US. Naval Weapons Laboratory, Dahlgren, Va. Filed Jan. 31, 1962, Ser. No. 170,194 9 Claims. (@l. 200-102) The present invention relates to a coaxial relay, and more particularly to a low-pass coaxial relay for protecting electrical or electronic systems from electrostatic and electromagnetic interference.

The instant invention solves the serious problem of damage caused by spurious energies induced in electronic circuits by electromagnetic and electrostatic fields. When used in a compatible electrical or electronic circuit the relay will not only provide virtually complete radio-frequency isolation up to the instant of relay operation but will also prevent premature functioning of the relay by radio-frequency energy above the pass-band. This solution is particularly important for providing adequate protection to weapon electroexplosive devices against electromagnetic and electrostatic fields.

The elimination of hazards of electromagnetic radiation to ordnance requires protection at all frequencies above a nominal. frequency in the region of 10 to 100 kilocycles per second. Further, the impedances of the spurious electromagnetic generators may have any value from a few tens of ohms to megohrns and will generally be complex.

It has been the practice to attempt to solve this problem by the use of conventional relays of coaxial or various other configurations. Conventional relays do not, however, provide satisfactory isolation of high energy RF fields because of inductive, capacitive or propagative coupling between contacts and other parts of the relay mechanism. That is, a relay contact is ineffective if it is situated in a circuit at a point of maximum voltage, minimum current, in a standing wave distribution. Unless the switch contacts are separated in a cut-off attenuator configuration of appreciable length propagative coupling may occur, even though the capacity between the contacts is very small. Under certain circumstances a switch may break a preexistent non-resonant circuit to form a high Q resonant system that is more readily energized by spurious RF energy at a particularly frequency. Conventional relays have the additional disadvantage that they may be operated, perhaps in an oscillatory manner, by RF power.

The instant invention accomplishes virtually complete RF isolation of the controlled circuit up to the instant of operation and prevention of premature operation of the relay by RIF energy above the pass-band. These characteristics are achieved, first by the use of a fast response double-action contact system which employs a heavy metal barrier in simultaneously open circuiting and blanking oil the coaxial line, and second, by placing the operating coil outside the coaxial line so as to produce a low-pass magnetic characteristic. Accordingly, it is an object of the present invention to provide interference protection against spurious energies induced by electromagnetic and electrostatic fields.

Another object is to provide a low-pass coaxial relay employing the intrinsic low-pass characteristics of a metal barrier in filtering out harmful energies.

A further object of the invention is the provision of a 1ow-pass coaxial relay employing an electromagnetic shield for attenuating the magnetic field of a coil.

Still another object is to provide a relay having virtually complete radio-frequency isolation up to the instant of operation.

Yet another object of the present invention resides in the provision of a relay having an operating coil outside of a coaxial line for achieving low-pass magnetic characteristics.

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A still further object is the provision of a fast response low-pass coaxial relay having a double action contact system which produces virtually complete radio-frequency isolation of the controlled circuit by having a coaxial line simultaneously open circuited and blanked off with a heavy metal barrier.

A yet further object of the invention is the provision of immunity against premature functioning of a relay by radio-frequency energy above the pass-band.

Yet a still further object of the invention is to provide a relay employing a thick metal barrier so that the electric field and the small magnetic field at the open-circuited end of the coaxial line are both attenuated to a very small value.

Yet still another object of the invention is the provision of a low-pass coaxial relay for achieving protection of Weapon electroexplosive devices against spurious energies induced in their associated circuits by electromagnetic and electrostatic fields.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a cross sectional view of the low-pass ooaxial relay of the invention; and

FIG. 2 is an electrical circuit diagram illustrating a use of the invention in a firing circuit.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views there is shown in FIG. 1 the lowpass coaxial relay of the instant invention having a heavy metal tube it) and an operating coil ll wound thereon. Tube lt'l may, for purposes of example, be constructed of brass. The coaxial inlet 12-, an inner conductor of a coaxial line connector, comprises a soft iron rod suitably threaded at its outer extremity and extending into cavity 18 of tube it). Rod 12 is connected to a soft iron fixed contact 13 which is cylindrical and has a cavity having internal threads for suitable connection with the rod 12. Between the fixed contact 13 and the body 19 is positioned a cylindrical insulating sleeve 14 for providing suitable electrical insulation therebetween.

The moving contact 15, or poppet valve, is made of soft iron and is suitably seated in valve seat 17 of the valve housing 2%. The valve housing Ztl is maintained in good electrical contact with the body Ill and may in fact be an integral part of the body ill. The valve housing sleeve 26 has a central cavity therethrough for extension therein of the moving contact 15 when suitably seated in valve seat 1'7. The moving contact 15 which extends partially through the cavity in the valve housing sleeve 29 has an elongated portion which is electrically separated from the valve housing sleeve Ztl by an insulating sleeve 21. The soft iron moving contact 15 is connected to the coaxial outlet 23, an inner conductor of a coaxial line connector, through a spring 22. Spring 22 may be a small beryllium copper spring which also serves to make contact with the center conductor of the outgoing coaxial circuit in addition to placing tension on the moving contact 15. The coaxial inner conductor 23 may for purposes of example, be constructed of brass but must be of non-ferromagnetic material.

In the inoperative condition, that is when the moving contact 15 has not traversed the air gap 16 to arrive at communicating juxtaposition with the face of the fixed contact 13, the relay contact system provides complete radio-frequency isolation by a combination of extreme boundary conditions. The coaxial inlet 12 is open circuited at its extremity because of the gap 16 between fixed contact 13 and moving contact 15. At this extremity of the line, the electric field vector predominates giving a high impedance point. it is assured that an absolute boundary condition for the principal coaxial mode of excitation exists at the end of the section of the line by means of a metal barrier across the tube comprising the valve seat and the valve head in the closed position. T heoretically, ignoring displacement current across the air gap at the open circuit, the thinnest possible metal film is suificient to set up the required boundary conditions. Thus,

n-D p where n is the unit normal directed from the metal surface into the air space Ezelectric field vector (intensity) D=electric displacement vector surface charge density However, to give greater assurance, the metal barrier in the instant application is made very thick so that the circumferential magnetic field associated with the small radial conduction current in the barrier caused by the small displacement current across the air gap is attenuated to a very small value.

On the other hand, satisfactory relay operation requires that a minimum axial flux be set up in the soft iron parts of the relay. This axial magnetic field, which can only be produced by the operating coil in the present invention, is attenuated in passing through tube 10 in accordance with the well known law of propagation in metals:

where y=propagation function u=attenuation function (nepers/meter) 13=phase function (radians/meter) u=initial permeability (henrys/meter) a conductivity (mhos/rneter) w=21r frequency in cycles per second from which is derived the equation for skin depth conditions. Under AC. conditions a simple attenuation =kv? relationship in the attenuation band exists where a constant determined by the metal used for construction of tube 19, and where f is frequency in cycles per second. Of course, this axial magnetic field cannot excite a principal coaxial mode in the protected section of the line. Such mode requires a circumferential magnetic field.

When the relay is powered by the alternating current of a frequency 1 within the pass-band the relay operates at if up to the limit of its mechanical response which would be 1640 cycles per second or a fundamental frequency of 820 cycles per second.

The power requirement for the relay is small enough to permit it to be energized by the ring circuit power and the voltage coil 11 may be connected directly across the firing circuit of an electroexplosive device or load squib. Once, however, the relay functions the low resistance of the electroexplosive device bridge wire will substantially short-circuit the voltage coil. For this reason, as best seen in FIG. 2, operating or voltage coil 11 is Cir a compound-wound type having a low impedance coil 24 and a high impedance coil 25 so that the magnetic flux thereof adds together. The low impedance coil 24 is connected in acres with the coaxial circuit, between fixed contact 13 through rod 12 and an input 35, of a firing circuit, and a high impedance coil 25 is connected between the input 34} and the shield connection 32 of the firing circuit, the shield connection 32 being either the outside casing of the relay unit (not shown) or the tube ill. Thus, the relay will hold over reliably during the firing pulse. The relay may, however, be operated from a separate supply to perform an arming function before firing.

The low-pass coaxial relay of the instant invention is particularly advantageous since inherent low-pass magnetic characteristics are achieved by having the operating coil 11 outside of the coaxial line. Further, the coaxial relay has a fast response and a double action contact systern which produces virtually complete radio-frequency isolation by having the coaxial line simultaneously open circuited and blanked with a heavy metal barrier.

in summarizing, the low-pass coaxial relay of the instant invention is capable of attenuating the axial alternating magnetic field produced by the operating coil Ill by virtue of the skin eifect of an electromagnetic shield. Further, the double action contact system of the instant invention provides, through the use of a very thick metal barrier, l5, l7 and 2d, a virtually complete elimination of the flow of radio-frequency energy from one contact to the other.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. .It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is desired to be secured by Letters Patent of the United States is:

l. A relay for providing radio-frequency isolation comprising an operating coil, means for physically supporting said operating coil and for attenuating the A.C. magnetic field thereof, means for providing an input to the relay, first relay contact means connected to said input means, means for providing an output from said relay, second relay contact means spaced from said first relay contact means, a thick metallic valve seat for seating said second relay contact means when said relay is in an inoperative condition, conductive resilient means connected between said second relay contact means and said output means for resiliently biasing said second relay contact means in an inoperable position whereby the radio-frequency axial magnetic field produced by said operating coil from spurious radio-frequency energy is attenuated and said valve seat and said second relay contact means provide radio-frequency isolation for the coaxial circuit.

2. A relay for providing radio-frequency isolation comprising an operating coil, a thick metallic tube for supporting said operating coil thereon and for attenuating the magnetic field of said operating coil, a fixed soft iron contact within said metallic tube, insulation means between said metallic tube and said fixed contact, input means connected to said fixed contact, a metallic barrier means for preventing radio-frequency energy from passing through the relay including a soft iron movable contact spaced from said fixed contact for traversing the space between said contacts for closing the relay in response to current flow through said operating coil and a thick metallic seat connected to the internal periphery of said metallic tube for seating said movable contact when said relay is in inoperative position, output means, and resilient means connected between said movable contact and said output means for resiliently biasing said movable contact in an inoperative position whereby said relay provides virtually complete radio-frequency isolation prior to the time of relay operation.

3. A relay as claimed in claim 2 wherein said metallic tube and said metallic seat are non-ferromagnetic.

4. A relay as claimed in claim 3 wherein said resilient means is electrically conductive.

5. A relay as claimed in claim 4 wherein said thik metallic seat comprises a valve housing with a beveled valve seat at a first extremity thereof and a cavity extending longitudinally therethrough and wherein said movable soft iron contact comprises a valve head portion formed for suitable seating on said beveled valve seat and an elongated portion for insertion into said housing cavity whereby said movable contact and said thick metallic seat form, during the inoperative condition of said relay, a thick metallic barrier for isolating radio-frequency energy.

6. A relay as claimed in claim 5 wherein said thick metallic seat is integral with the internal periphery of said metallic tube.

7. A relay as claimed in claim 6' wherein said input means comprises a coaxial connector having an externally threaded inner conductor and wherein said fixed contact comprises an internally threaded cavity extending longitu-dinally through a portion of said fixed contact from a longitudinal extremity thereof for connection with said externally threaded inner conductor of said input means.

8. A relay as claimed in claim 7 wherein said coil further comprises a low impedance coil connected in series with said inner conductor of said coaxial connector, and a high impedance coil connected between said metallic tube and the other end of said low impedance coil from said inner conductor.

9. A relay for providing radio-frequency isolation comprising an operating coil; a thick brass tube for supporting said operating coil thereon and for attenuating the magnetic field of said operating coil from spurious radiofrequency energy; a fixed soft iron contact Within said tube having an internally threaded cavity extending longitudinally through a portion of said fixed contact from a longitudinal extremity thereof; an insulative sleeve between said brass tube and said fixed contact; a coaxial input having an externally threaded inner conductor extending longitudinally into a first extremity of said brass tube and connected to the internally threaded fixed contact; a brass housing having a thick beveled valve seat, a cavity extending longitudinally through said valve seat, and a movable soft iron contact having a valve and an elongated portion for insertion into said housing cavity; a coaxial output having an inner conductor extending longitudinally into a second extremity of said brass tube; and a beryllium copper spring connected between said movable contact and said output for providing a conductive path and for spring biasing said movable contact away from said fixed contact whereby the radio-frequency axial magnetic field produced by said operating coil is attenuated and said beveled valve seat and said moving contact form a metal barrier for providing radio-frequency isolation for the coaxial circuit.

References {Iited in the file of this patent UNITED STATES PATENTS 

1. A RELAY FOR PROVIDING RADIO-FREQUENCY ISOLATION COMPRISING AN OPERATING COIL, MEANS FOR PHYSICALLY SUPPORTING 